I recently bought a Linksys WRT-54GL router and a DSL router/modem so I
could have a good network setup for my home computers/server. I must
admit that configuring all that is rather hard if you don’t know much
about networking, so I decided to write this “Networking essentials”
guide so people could have an idea what all these terms
mean.

IP (Internet Protocol) Address

First off, a bit about IP addresses. In order for computers to talk to
each other, they must have a way to address each other, so each one
needs to have a unique name (or number). Since, however, numbers are
more practical for computers, that’s what we use. A computer’s number is
its IP address, and it’s unique to it within a network (so yes, noone on
the entire internet in the whole world has the same IP address as you.

An IP address consists of four numbers (they’re actually four digits,
but don’t pay much attention to this) in the range 0-254, separated by
periods. So, 119.12.23.64 is a valid IP address (and someone is probably
using it right now).

DNS (Domain Name System) server

As I already said, the internet works with IP addresses, and that’s how
your computer knows where to get what you want. IP addresses, however,
are rather tedious for people to remember (it’s much easier to remember
poromenos.org than 63.247.68.107), so we need a system to translate
human-readable words into IP addresses. This is what the DNS does. When
you type a hostname (such as www.poromenos.org) in a program, your
computer sends a DNS request to its DNS server to ask it what IP address
that hostname corresponds to. The DNS server checks its list for the
address. If it doesn’t know it, it forwards the request to another DNS
server. This can take a few hops if noone knows the hostname, until the
request reaches the root servers, which hold all the hostnames in the
world. If the address isn’t found there either, the lookup fails.

DHCP (Dynamic Host Configuration Protocol) Server

The DHCP server’s job is to send the network configuration to any client
that requests it. So, instead of setting each computer’s IP address, DNS
server, gateway, etc manually, your computer sends a DHCP request and
all this info is returned to it by the server. For IP addresses, the
DHCP server has a list of addresses it has leased to computers (they are
leased because they expire after a few days, usually, and need to be
renewed), to make sure it doesn’t assign the same address to two
computers.

Gateway

The gateway is a computer (or device) that connects a network to another
network, for example your LAN to the internet. Computers send their
requests to the gateway and the gateway forwards them to the internet
and relays the responses back.

Ports

Each computer has various ports (65536, to be exact) on which it can
receive data. This is purely for convenience, since this way computers
can offer various services on specific ports. For example, if you
connect to some computer’s port 80, you’ll find its web server (if it
has one). Similarly, port 110 is POP3 (for getting your e-mails), 25 is
SMTP (for sending your e-mails), etc.

This list is rather small now, but if there’s anything else you’d like
to know, post a comment here and I’ll add it if it’s pertinent.

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